The present invention relates to rotary regenerative heat exchangers and, more particularly, to an apparatus for accurately determining the amount of turndown of the rotor during operation of the rotary regenerative heat exchanger.
In a rotary regenerative heat exchange apparatus such as an air preheater, a mass of heat absorbent material commonly comprised of packed plate-like elements carried in a rotor shell is alternately positioned first in a hot fluid passageway and then in a cold fluid passageway as the rotor shell rotates about a central rotor shaft. At one position in the hot fluid passageway, the heat absorbent material absorbs heat from the hot fluid passing therethrough. After the heat absorbent material has been heated by the hot fluid, it is positioned in a cold fluid passageway where the then hot heat absorbent material transmits its heat to the cold fluid passing therethrough. A fixed housing, including sector plates disposed at opposite ends of the rotor, is adapted to surround the rotor shell wherein the heat absorbent material is carried. To prevent intermingling of the hot fluid and the cold fluid as they pass through the heat exchange apparatus, the sector plates are adapted to lie in sealing relationship with flexible radial seals mounted on the end faces of the rotor shell at spaced intervals about the central rotor posts. Additionally, axial seals are provided at the outboard circumferential surface of the rotor shell to prevent the hot fluid or the cold fluid from bypassing the heat absorbent material carried within the rotor shell.
In a standard rotary heat exchange apparatus such as the air preheater described herein, the hot fluid, hereinafter referred to as the hot gas, and the cold fluid, hereinafter referred to as cold air, enter the rotor shell from opposite ends and pass in opposite directions over the heat exchange material housed within the rotor shell. For example, if such a heat exchange apparatus is disposed horizontally to rotate about a vertical shaft, the hot gas enters the top of the heat exchanger and flows vertically downward through one side of the rotor, transferring its sensible heat to the heat absorbent material rotating therethrough with the cooled gas exiting at the bottom of the heat exchanger. At the same time, cold air enters the bottom of the heat exchanger and flows vertically upward through the other side of the rotor picking up sensible heat from the heat absorbent material rotating therethrough with the heated air exiting at the top of the heat exchanger.
Inasmuch as the cold air inlet and the cooled gas outlet are at the bottom of the heat exchanger and the hot gas inlet and the heated air outlet are at the top of the heat exchanger, an axial temperature variation exists within the rotor shell with the top end of the rotor being the hot end and the bottom end of the rotor being the cold end. In response to this thermal gradient, the rotor tends to "turndown," i.e., to distort and assume a shape similar to that of an inverted dish. As a result of such a turndown, the radial seals mounted on the upper and lower surfaces of the rotor, i.e., the hot end, are pulled away from the sector plate with the greatest separation occurring at the outboard end of the rotor, thereby allowing fluid leakage therebetween resulting in the undesired intermingling of gas and air.
Various schemes of compensating for the loss of sealing effectiveness at the hot end of the rotor as a result of "turndown," such as U.S. Pat. No. 3,786,868 and U.S. Pat. No. 4,124,063, have been proposed wherein the upper sector plate is adjusted, i.e., bent downward, to recontact the radial seals mounted on the upper surface of the rotor. However, before the sector plate is adjusted, it is desirable to know the amount of turndown, particularly at the outer end of the rotor so that the radial seals will not be damaged by an operator who unknowingly overcompensates for the turndown. In the past, a spring loaded rod was commonly used to detect the position of the radial seals with respect to the sector plate after rotor turndown. The operator would manually push the rod against the force of the spring into contact with the radial seals and take a measurement of the linear displacement of the rod as a means of indicating the amount of turndown. Upon releasing the rod, the spring would recoil and return the rod to its normal position. In many instances, however, the operators would inadvertently continue to push the rod inward without realizing the rod had made contact with the radial seals resulting in the seals being damaged or the rods being bent and thus rendered inoperative.